[R-390] AN/URM-25s

[2002tii]

Dennis wrote:

>I think by the radio leaking, he means that the radio will pick up/be
>sensitive to signals coming in through paths other than the antenna
>connector/antenna circuit.

Exactly.  Signals getting out of a box other than through the 
intended port, and signals getting into a box other than through the 
intended port, are both leakage.  When you are trying to measure the 
maximum sensitivity of a radio, it is a problem if your sig gen 
"leaks out" and your receiver "leaks in."  [This is because the 
signal that leaks out of the sig gen leaks into the radio, so the 
actual signal the radio is receiving -- some through the antenna 
connector plus some by leakage -- is stronger than the signal the 
generator is putting into the receiver's antenna terminal.  If you 
think that what is going into the antenna input is all there is, you 
will be fooled into thinking that your radio is more sensitive than 
it really is.]

Of course, "leakage out" and "leakage in" go hand in hand -- if there 
is a leakage path in, there is also a leakage path out, and 
vice-versa.  But *when we are measuring receiver sensitivity,* we 
generally do not care about RF energy getting out of the radio 
because it generally does not disturb our measurements (regenerative 
receivers, direct conversion receivers, and receivers with very high 
RF gain and poor shielding of the RF section are exceptions).  We may 
or may  not care about signals getting into the sig gen, depending on 
what mischief they cause (do they come out of the sig gen output?  do 
they cause distortion or spurious responses?  etc.).

On the other hand, if we are trying to be stealthy (i.e., not give 
our position away to hostile forces who are using an RF "sniffer" to 
detect the leakage out of our radios), we may care very much about 
signals getting out of our receiver.  The military has a number of 
qualification programs concerning "compromising emissions," the 
best-known of which is the TEMPEST program (which covers mechanical 
and acoustical emissions in addition to electromagnetic 
emissions).  The Harris 590's admirable "leakage in" performance is 
actually a result of the great care the designers took to prevent 
"leakage out."

Best regards,

Don


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